The SSPX is essentially apostolic, because such is the Sacrifice of the Mass
As a rule the members of the SSPX exercise an exterior apostolate. They live with the conviction that the whole efficacy of their apostolate flows from the Sacrifice of Our Lord, which they offer every day and around which all apostolic initiatives are organized.
Men and women join the work of the priests and sanctify themselves in prayer and in multiple apostolic endeavors. Some of which are more inspired by the contemplative life, others want to actively engage in works of charity of all sorts. All of them strive to promote the Kingdom of Christ and the sanctification of the souls.